Beschreibung
Mucins are a family of water soluble, and heavily glycosylated, proteins which, as the major macromolecular constituent of mucous, have a general function in forming wet physiologically relevant chemical and physical barriers in animals.1 Apart from the ability to form limited cross-links, gelation behavior, an important structure motif is the bottle-brush structure formed by the pendant glycosylations around the extended unfolded protein core consisting largely of serine and threonine. At neutral pH the glycosylations are largely uncharged. In this study we aim understand the dynamics of the water binding to the glycosylations in water, and eventually the coupling of water binding to the overall flexibility of the mucin backbone through the excluded volume interactions between the hydrated pendant glycosylations. Biological variability is often a problem for the relevance of these studies, for this reason we have utilized a commercial product available as lyophilized powder, pig gastric mucin (PGM). Differential scanning calorimetry (DSC) results suggest that the PGM can hold approximately 0.51 g of bound water per g of dry PGM.2 At this moisture content it is suggested that there is glass transition at approximately 25oC. Our initial studies on temperature dependance of QENS using hydrated powders of PGM below a moisture content suggest by DSC with the direct geometry time of flight spectrometers: FOCUS (Paul Scherrer Institute, Villigen, Switzerland); and IN5 (Institute Laue-Langevin, Grenoble France). The IN5 samples consisted of pairs of matched hydration where all available exchangeable H has been exchanged with D by exchange with D2O and samples prepared in natural abundance H2O. Together with fixed elastic window scans on the thermal backscattering spectrometer IN13 (Institute Laue-Langevin, Grenoble France) we are able to demonstrate a layer of water which is strongly coupled to the dynamics of the pendant glycosylations on the mucin backbone.
